1. Open the Snapchat app and find a conversation someone sent to you that you want to read (without them knowing).
2. SLOWLY swipe right on the conversation and hold down on the screen. DO NOT release your finger. DO NOT swipe all the way right!
3. As soon as you see part of the conversation, continue to swipe slowly while holding down UNTIL there is a small border (pictured below) at the right of the screen. You will only be able to read this much of the conversation.
If you swipe all the way right, you will have read the conversation and the sender will be notified.